Optical video discs provide a means of distributing movies and other programming in a pre-recorded format for on-demand viewing on a television receiver. When played on a suitable device, a video disc produces a standard television signal (NTSC, PAL, etc.) which can be displayed on a television receiver or monitor. This signal can also be recorded on any standard video tape recorder (VHS, Beta, 3/4 inch, U-Matic, etc.). As such, copies of any pre-recorded program can be easily and inexpensively made.
With the vast number of video tape recorders (VTR's) now in use, it has become commonplace for users to record off-the-air television programs for subsequent and repeated viewing. In addition, consumers have enthusiastically embraced pre-recorded video programming, typically commercially successful motion pictures; and this has resulted in large libraries of pre-recorded video tapes for sale or rent to the public. The profit associated with selling o renting these pre-recorded video tapes has spawned large scale video tape piracy. Such "pirates" reproduce hundreds or thousands of unauthorized copies of a single pre-recorded program on video tape. This deprives the rightful owners or distributors of the programs of their lawful income. Since currently, the programs on optical video discs are freely recordable by VTR's this represents an easy source for pirates.
Optical video discs are manufactured by molding a plastic material in a press, much as standard phonograph records are made. Signal information is put on the disc in a spiral pattern analogous to the spiral groove of a phonograph record in the form of tiny pits. The pits form a representation of a frequency. This frequency is modulated by the video signal and, by using an FM detector in the player, the original video signal is recovered.
Optical video discs are made in two formats: "constant angular velocity"; and "constant linear velocity". In the first case the turntable motor operates at constant speed such that the linear velocity between the information path and the transducer is greatest at the outside of the disc and gradually decreases as playback proceeds along the spiral towards the center of the disc. In the second case the turntable motor speed varies with the radial position of the transducer, such that a constant linear velocity is maintained between the information path and the transducer. This requires the turntable speed to steadily increase as playback proceeds along the spiral path towards the center of the disc. The methods of the present invention can be applied to both formats.